1. Field of the Invention
This invention relates to tachometers in general and more particularly to a digital tachometer for an object for counting down along a stepped approximation to a 1/t curve to determine velocity as a function of the count accumulated during an interval of displacement of the object.
2. Description of the Prior Art
The prior art tachometers which are actuated by pulses representing travel over a predetermined distance can be separated into two groups. The first group counts the number of pulses received over a fixed time interval and presents the output as a frequency which must be converted to a digital velocity by scaling or as an analog voltage from a frequency-to-voltage converter. The major disadvantage of this type of tachometer is that it is limited to applications which do not require the rapid recognition of a change in velocity since the response time is determined by the fixed time interval and the time interval must be long enough to accumulate enough pulses to provide adequate resolution at low values to velocity.
The second group of tachometers utilizes the distance input pulse to trigger a high frequency pulse train wherein the high frequency pulses are accumulated until the next input pulse stops the counting. The major disadvantage of this type of tachometer is that the accumulated count represents time which must be divided into the predetermined distance and a digital division is difficult to make.